Process of coating fiberboard and resulting product



United States atent 3,281,252 PROCESS OF COATING FIBERBOARD ANDRESULTING PRODUCT William P. Fairchild, San Diego, Calif assignor toKelco Company, San Diego, Calif., a corporation of Delaware No Drawing.Filed Mar. 29, 1965, Ser. No. 443,689 8 Claims. (Cl. 106-15) Thisinvention relates to fire retardant coatings for structural panels ofcompressed fiber, and to the resulting products.

This application is a continuation-in-part of my application entitledProcess of Coating Fiberboard and Resulting Product, Serial No. 148,695,filed October 30, 1961.

A common structural panel or board widely used in building and likeconstruction is formed by compressing vegetable fibers so as to producea porous but structurally rigid panel member, which may be used as wallboard, as thermal and acoustic insulation panels on or in partitions, assub-flooring, on or in ceilings, and the like. A particular type of thisproduct is punched with a plurality of holes, commonly to inch indiameter, which penetrate one surface to a short distance, and rendersthe product especially useful in the acoustic treatment of enclosures,where it is desirable to reduce echo.

A wide variety of vegetable fibers is used in the manufacture of panels,boards, acoustical tiles, and like products, all of which arehereinafter occasionally referred to as porous compressed vegetablefiber structural panels. One especially widely used product of this typeis made from the refuse of sugar cane refining, known as bagasse. Ingeneral, the bagasse is shredded so as to separate the individual fibersof the cane sugar stock, to a greater or less extent, and the mattedfibers, with or without the addition of paper pulp, ground newspapers,and the like, are compressed to give a structural panel with flat sides,generally about /2 inch in thickness. Panels for acousticaluse andthermal insulation use are commonly made thicker, as much as one inch.Various bark fibers may also be used such as the bark of redwood,Douglas fir, and like trees. Corn stalks are another source of vegetablefibers for the manufacture of structural panels of the type described.As mentioned, structural panels of this type are porous, that is, theywill absorb water, and have some permeability to the passage of air,although this may be rather low. However, they form a distinct classfrom panel boards made, for example, by admixing sawdust with a binderand treating under high temperatures and high pressures so as to producean impervious, dense board of even greater density than the originalwood from which the sawdust was derived.

As may readily be understood, structural panels of the type describedand to which this invention is directed are subject to combustion, andoffer no more resistance to fire than wood itself. It is highlydesirable to treat porous compressed vegetable fiber structural panelsso as to render them fire resistant. A number of treating agents areknown for this purpose, applicable to wood, paper, draperies, and thelike, and all belonging in general to a class of chemicals, generallysalts and especially inorganic salts, which are more or less soluble inwater, so that the articles to be treated may be sprayed with or dippedin a solution of the chemical in question, whereupon the water isallowed to evaporate and a fire resistant chemical thereby incorporatedin and on the treated article.

It is a fact, however, that surface treatment is of greater importancethan treatment in depth, that is, throughout the body of an article suchas the porous structural panels described, since before the interior ofsuch an article can burn, it is necessary for the surface to burn first.Thus, save the surface and you save all is highly applicable to thepanels in question.

Great difficulty has been encountered in the past in applying fireretardant treatments to porous compressed vegetable fiber structuralpanels, because the very nature of these articles causes them to soak upthe liquid applied, and there is no surface concentration of the fireretardant chemical, but the latter is rather distributed throughout thebody of the panel. In order to achieve satisfactory fire resistance, itis necessary to increase greatly the amount of chemical applied, overwhat would be necessary if the chemical could be concentrated in thesurface layer. Not only does this lead to excessive treating costs, butthe Weight of the panel is unduly increased because of the burden oftreating chemical which it takes up, and moreover its insulatingcapacity, both thermal and acoustic, is reduced, because of the greateramount of total solids per cubic inch of material.

An object of the resent invention is to provide a fire retardanttreating solution and a process of applying the same to porouscompressed vegetable fiber structural panels so as to result in asurface concentration of the treating agent.

Another object of the invention is to provide a porous compressedvegetable fiber structural panel having a surface concentration of fireretarding agent.

Other objects of the invention will appear as the description thereofproceeds.

Generally speaking, and in accordance with an illustrative embodiment ofmy invention, I prepare an aqueous solution of any selected fireretardant chemical, generally making as concentrated a solution aspossible, and incorporate with the said solution a modicum, typically to1%, of a Xanthomonas colloid produced by the bacterium Xanthomonascampestris.

In the aforementioned example of my invention employing a Xanthomonashydrophilic colloid, I referred to such a colloid produced by thebacterium Xanthomonas campestris. This colloidal material is a polymercontaining mannose, glucose, potassium glucuronate and acetyl radicals.In such a colloid, the potassium portion can be replaced by severalother cations without substantial change in the property of the saidmaterial for my purpose. The said colloid, which is a high molecularweight, exocellular material, may be prepared by the bacteriumXanthomonas campestris, by whole culture fermentation of a mediumcontaining 2-5 percent commercial glucose, organic nitrogen source,dipotassium hydrogen phosphate and appropriate trace elements. Theincubation time is approximately 96 hours at 28 C. aeroblc conditions.In preparing a Xanthomonas colloid as aforesaid, it is convenient to usecorn steep liquor or distillers dry solubles as an organic nitrogensource. It is expedient to grow the culture in two intermediate stagesprior to the final inoculation in order to encourage vigorous growth ofthe bacteria. These stages may be carried out in media having a pH ofabout 7. In a first stage a transfer from an agar slant to a diluteglucose broth may be made and the bacteria cultured for 24 hours undervigorous agitation and aeration at a temperature of about 30 C. Theculture so produced may then be used to inoculate a higher glucose (3%)content broth of larger volume in a second intermediate stage. In thisstage the reaction may be permitted to continue for 24 hours under thesame conditions as the first stage. The culture so acclimated for usewith glucose by the aforementioned first and second stages is then addedto the final glucose medium. In the aforesaid method of preparing aXanthomonas cnmpestris hydrophilic colloid, a loopful of organism fromthe agar slant is adequate for the first stage comprising 200milliliters of the said glucose media. In the second stage the materialresulting from the first stage may be used together with 9 times itsvolume of a 3% glucose media. In the final stage the material producedin the second stage may be admixed with 19 times its volume of the finalmedia. A good final media may contain 3% glucose, 0.5% distillers drysolubles, 0.8% d-ipotassium phosphate, 0.1% magnesium sulphate having 7molecules of water of crystallization and water. The reaction in thefinal stage may be satisfactorily carried out for 96 hours at 30 C. withvigorous agitation and aeration. The resulting Xanthomonas campestrz'scolloidal material which I have found to be particularly suitable for mypurpose can be recovered by precipitation in methanol of the clarifiedmixture from the fermentation. This resulting material may also bedesignated as a pseudoplastic, heteropolysaccharide hydrophilic colloidor gum produced by the bacterium species 1 X anthomonas campestris.

Other suitable Xanthomonas colloidal material may be prepared byrepeating the procedure used for producing the X anthomonas campestri'scolloidal material by substituting known Xanthomonas bacterium ororganisms, i.e., Xanthomonas carotae, Xanthomonas incanaea, Xanthomonaspz'si, Xanthomonas begoniae, and Xanthomonas malvacearum, for thebacterium, Xanthomonas campestris.

The fire retardant chemicals which may be used are those common in theart, and include boric acid, borax, sodium metaborate (or, what amountsto the same material, equimolar quantities of boric acid and borax),sodium calcium borate, especially as the mineral boronatrocalcite, thenative sodium borate known as rasorite, ammonium sulfamate, secondaryammonium phosphate, sodium phosphate, sodium silicate, ammonium sulfate,equimolar mixtures of zinc chloride and sodium dichromate, and likematerials. These are all soluble in water, and in general theirsolubility increases wtih increasing temperatures, so that in order toreduce the amount of water which must be subsequently evaporated off soas to leave a given weight of chemical, it is desirable to use asaturated solution, not merely saturated at room temperature butsaturated at elevated temperatures, for example, 60 C. to 100 C. Theconcentrations of the fire retardant chemicals used thus, it will beclear, will depend upon the particular chemical chosen, its solubilityin water, and the temperature at which the solution is prepared.

As mentioned, I use from about to 1% of a Xanthomonas colloid, forexample, a Xanthomonas campestrz's hydrophilic colloid, based on a totalweight of treating solution, the latter comprising water and theselected chemical or indeed mixture of chemicals.

Like formulations to the above substituting the Xanthomonas colloidalmaterial produced by the other aforementioned Xanthomonas bacterium,produced comparable results in accordance with my invention. However,the quantity of the Xanthomonas colloid should be varied depending uponthe species thereof. More particularly, when using a Xanthomonas colloidproduced by the organ-isrn Xanthomonas carotae, 1.9 parts of saidcolloid should be substituted for each part of a colloid produced by thebacterium Xanthomonas campestris. Similarly, when substituting thecolloid produced by the bacterium Xanthomonas incanaea, 1.5 parts arerequired. When substituting Xanthomonas begoniae, 1.65 parts arerequired. When substituting Xanthomona's pisi, 1.25 parts are required,and when substituting Xanthomonas malvacearum, 1.25 parts are required.

Treating compositions made up in accordance with my invention have theastonishing property of exhibiting minimal penetration into porouscompressed vegetable fiber structural panels, when applied to surfacesof the latter. I do not wish to be bound by any theory of operationadvanced and indeed I have not'been able to determine all of the factorswhich contribute to this remarkable property, but it seems to beassociated with the nature of the gel formed when the colloid is added,and the fact that the gel nature is unaffected by the presence of thechemicals or even of the combination of the chemicals and the hightemperatures which may be and preferably are used.

Examples of my invention will now be given:

Examples To 183 parts of water I added one part of Xanthomonascampestris hydrophilic colloid prepared as described hereinabove. I thenheated this to F., and dissolved 16 parts of boric acid therein, to forma treating solution in accordance with the invention. Next, I appliedthis solution, using a laboratory coating bar, to a porous compressedvegetable fiber structural panel made from bagasse, having a totalthickness of /2 inch, and sold under the trade name Celotex. The treatedboard was all-owed to stand for 72 hours after which time it was dry.

This treated structural panel was then subjected to scorch tests byapplying a steel plate thereto heated to 250 C. The scorch resistance ofthis panel treated in accordance with the invention with the Xanthomonascampestris colloid was very good.

Boric acid solutions of 2%, 5%, and 10% containing 0, 0.1%, 0.3%, 0.75%,and 1% of a Xanthomonas campestris hydrophilic colloid were prepared inthe manner described in the example.

These solutions were stored for one week at 140 F. in tightly-cappedbottles. They were then used to coat portions of insulating board whichhad been formed but not dried on the machine during manufacture. Thatis, the board Was in the same wet condition as is the same board on themachine ahead of the drying section. The coated portions of board werethen placed under an infra-red lamp which supplied a surface temperatureof 187 C. After 1.5 hours the surface of the board samples was dry. Thedegree of surface scorch of the various samples was compared with thatof uncoated board.

The degree of scorch and fiber toasting was found to be in directrelation to both the concentration of boric acid and the concentrationof the Xanthomonas campestris hydrophilic colloid in the coating. Forexample, at each X anthomonas campestris hydrophilic colloid levelscorch decreased with increasing boric acid concentration. Likewise, fora given boric acid level, scorch and fiber toasting decreased withincreasing Xanthomonas colloid concentration.

It will be found that when repeating the above examples substitutingother Xanthomonas colloids for the Xanthomonas campestris colloid,comparable results will be obtained, particularly when adjusting thequantities in keeping with the disclosure heretofore made in saidregard.

While I have described the invention in terms of specific materials,treating agents, treating conditions and the like, it is to beunderstood that the invention is a broad one, and numerous variations ofdetail may be made in carrying it out, all within the scope of theclaims which follow.

What I claim is:

1. A treating solution adapted for coating porous compressed vegetablefiber structural panels comprising water from about to 1% of ahydrophilic gum colloid produced by a gum producing bacterium of thegenus Xanthomonas, and a saturating amount of a fire retardant materialselected from the class consisting of boric acid, sodium metaborate,sodium calcium borate, ammonium sulfamate, ammonium phosphate, sodiumphosphate, sodium silicate, ammonium sulfate and an equimolar mixture ofzinc chloride and sodium dichromate.

2. The composition of claim 1 wherein said hydrophilic colloid isproduced by the bacterium Xanthomonas campestris.

3. The composition of claim 1 wherein said hydrophilic colloid isproduced by the bacterium Xanthomonas pm.

4. The process of treating a porous compressed vegetable fiberstructural panel which comprises applying to at least one surfacethereof a treating solution consisting essentially of water, a watersoluble :fire retardant material, and a small amount ranging from aboutto 1% of the treating solution of a hydrophilic colloid produced by abacterium selected from the group consisting of Xanthomonas carotae,Xanthomonas incanae, Xanthomonas pisi, Xanthomonas begoniae, Xanthomonasmalvacearum, and Xanthomonas campestris, said amount of colloid beingsufiicien-t to cause the said fire retardant material to concentrate inand adjacent the treated surface of said panel and subsequently allowingthe so-treated panel to dry by evaporation of the Water contained insaid treating solution.

5. The process of claim 4 wherein said hydrophilic colloid is producedby the bacterioum Xanthomonas campestris.

6. The process of claim 4 wherein said hydrophilic colloid is producedby the bacterium Xanthomonas pisi.

7. The process of claim 4 wherein said fire retardant material is chosenfrom the class consisting of boric acid, borax, sodium metaborate,sodium calcium borate, am-

References Cited by the Examiner UNITED STATES PATENTS 2,769,729 11/1956Van de Zande 106-15 XR 2,889,235 6/1959 Campbell et al. 10615 XR3,000,790 9/ 196-1 Jeanes et al. 3 1 3,020,206 2/1962 Patton et al.10615 3,054,689 9/1962 Jeanes et al. 106-208 3,096,293 7/1963 Jeanes etal. 106209 XR OTHER REFERENCES Information on Polysaccharide, CA-N-9,September 1959; CA-N-14, April 1961; and CA N-Zl, May 1962, U.S. Dept.of Agriculture Research Service, Northern Utilization Research andDevelopment Div.

ALEXANDER H. BRODMERKEL, Primary Examiner.

J. B. EVANS, Assistant Examiner.

1. A TREATING SOLUTION ADAPTED FOR COATING POROUS COMPRESSED VEGETABLEFIBER STRUCTURAL PANELS COMPRISING WATER FROM ABOUT 1/10 TO 1% OF AHYDROPHILIC GUM COLLOID PRODUCED BY A GUM PRODUCING BACTERIUM OF THEGENUS XANTHOMONAS, AND A SATURATING AMOUNT OF A FIRE RETARDANT MATERIALSELECTED FROM THE CLASS CONSISTING OF BORIC ACID, SODIUM METABORATE,SODIUM CALCIUM BORATE, AMMONIUM SULFAMATE, AMMONIUM PHOSPHATE, SODIUMPHOSPHATE, SODIUM SILICATE, AMMONIUM SULFATE AND AN EQUIMOLAR MIXTURE OFZINC CHLORIDE AND SODIUM DICHROMATE.
 4. THE PROCESS OF TREATING A POROUSCOMPRESSED VEGETABLE FIBER STRUCTURAL PANEL WHICH COMPRISES APPLYING TOAT LEAST ONE SURFACE THEREOF A TREATING SOLUTION CONSISTING ESSENTIALLYOF WATER, A WATER SOLUBLE FIRE RETARDANT MATERIAL, AND A SMALL AMOUNTRANGING FROM ABOUT 1/10 TO 1% OF THE TREATING SOLUTION OF A HYDROPHILICCOLLOID PRODUCED BY A BACTERIUM SELECTED FROM THE GROUP CONSISTING OFXANTHOMONAS CAROTAE, XANTHOMONAS INCANAE, XANTHOMONAS PISI, XANTHOMONASBEGONIAE, XANTHOMONAS MALVACEARUM, AND XANTHOMONAS CAMPESTRIS, SAIDAMOUNT OF COLLOID BEING SUFFICIENT TO CAUSE THE SAID FIRE RETARDANTMATERIAL TO CONCENTRATE IN AND ADJACENT THE TREATED SURFACE OF SAIDPANEL AND SUBSEQUENTLY ALLOWING THE SO-TREATED PANEL TO DRY BYEVAPORATION OF THE WATER CONTAINED IN SAID TREATING SOLUTION.